Studies will be undertaken on the mechanism of action of ethanolamine ammonia-lyase, a B12-requiring enzyme that catalyzes the conversion of certain vicinal amino alcohols to oxo compounds and ammonia. Experiments with alternative substrates and substrate analogs will be carried out to investigate the mechanism of catalysis, directing particular attention to the question of how the amino group migrates. Amino acid residues at the active site will be identified by covalent modification, using for this purpose both group-specific and affinity labels. The structure of the enzyme will be determined, using gene cloning and sequencing techniques to determine the amino acid sequence in the two subunit classes, and X-ray crystallography to ascertain the 3-dimensional structure of the enxyme. These studies should provide insights into the biochemical role of B12 (cobalamin), an essential trace component of the human diet.